1. Field of the Invention
The present invention relates to an image display device constructed by using an electron source and a method of manufacturing the display device.
2. Related Background Art
In a device which displays an image using a phosphor that serves as an image display member and emits light when irradiated with an electron beam from an electron source, the vacuum level in the interior of a vacuum container that houses the electron source and the image display member has to be kept high. This is because gas generated in the vacuum container raises the pressure and adversely affects the electron source, though the degree of adverse affect varies depending on the type of gas, to lower the electron emission amount and the brightness of a displayed image. In addition, gas generated in the vacuum container could be ionized by the electron beam and the resultant ion is accelerated by an electric field, which is for accelerating electrons, to bump and damage the electron source. Furthermore, in some cases, gas in the vacuum container induces electric discharge that can destroy the whole display device.
Usually, a vacuum container of an image display device is obtained by combining glass members and bonding them at the juncture with flit glass or the like. Once the joining is completed, the pressure is maintained by a getter set in the vacuum container.
In a normal CRT, an alloy mainly containing Ba is energized or heated using high frequency wave in a vacuum container to form a thin evaporation film on the inner wall of the container. The evaporation film adsorbs gas generated in the vacuum container and the high vacuum level is thus maintained.
Lately, development of a flat panel display with an electron source that has a large number of electron-emitting devices arranged on a flat substrate has been advanced. In ensuring the vacuum level, gas generated from an image display member reaches the electron source before dispersed and sent to a getter to thereby cause a local pressure rise and resultantly degradation of the electron source, which is a problem characteristic to this type of display.
In order to solve this problem, a specific structure for a flat panel display has been disclosed in which gas is adsorbed, as soon as it is generated, by a getter material placed in an image display region.
For instance, Japanese Patent Application Laid-Open No. 04-12436 discloses a method of forming from a getter material a gate electrode which is provided in an electron source to extract an electron beam. Shown as examples in this publication are a field emission type electron source that uses a conical protrusion for a cathode and a semiconductor electron source having a pn junction.
Japanese Patent Application Laid-Open No. 63-181248 discloses a method of forming a getter material film on a control electrode, namely, an electrode (grid or the like) for controlling an electron beam, which is placed between a cathode group and a face plate of a vacuum container in a flat panel display.
U.S. Pat. No. 5,453,659 (Anode Plate for Flat Panel Display having Integrated Getter, issued 26 Sep. 1995 to Wallace et al.) discloses a display in which getter members are formed in gaps between phosphors that form a stripe pattern on an image display member (anode plate). In this example, a getter material is electrically isolated from a phosphor and from a conductor that is electrically connected to the phosphor. An appropriate electric potential is given to the getter to radiate and heat electrons emitted from an electron source, and the getter is thus activated.
For an electron-emitting device which constitutes an electron source for use in a flat panel display, obviously one having a simple structure easy to fabricate is desirable in light of production technique, manufacturing cost, and the like. Specifically, an electron-emitting device that is in demand is one whose manufacturing process consists of layering thin films and simple working or, if a large-sized electron source is to be obtained, one manufactured by printing or other technique that does not need a vacuum device.
The above electron source, which is disclosed in Japanese Patent Application Laid-Open No. 04-12436 and which has a gate electrode formed from a getter material, requires laborious processes inside a vacuum apparatus in manufacturing a conical cathode chip or in joining the semiconductors. Furthermore, its manufacturing apparatus puts limitations on making this electron source larger.
As to the display device which is disclosed in Japanese Patent Application Laid-Open No. 63-181248 and which has a control electrode between an electron source and a face plate, the structure is complicated and the manufacturing process entails laborious processes such as positioning of those members.
The method disclosed in U.S. Pat. No. 5,453,659, in which a getter material is formed on an anode plate, needs electric insulation between the getter material and a phosphor and requires a large-sized photolithography device for precise, minute working. Accordingly, an image display device manufactured by this method is limited in size.
In contrast, a lateral field emission type electron-emitting device and a surface conduction electron-emitting device are electron-emitting devices that meet the above demand, namely, to have a structure easy to fabricate.
A lateral field emission type electron-emitting device has, on a flat substrate, opposing cathodes (gates) that are provided with pointed electron-emitting regions. A thin film deposition method such as evaporation, sputtering, or plating and a normal photolithography technique are employed to manufacture a lateral field emission type electron-emitting device.
A surface conduction electron-emitting device emits electrons by letting a current flow in a conductive thin film a part of which is a highly resistant portion.
An electron source using a lateral field emission type electron-emitting device and an electron source using a surface conduction electron-emitting device have neither the gate electrode shaped as disclosed in JP 04-12436 A nor the control gate disclosed in Japanese Patent Application Laid-Open No. 63-181248. Placing a getter in an image display region by a method similar to the one in those publications is therefore not an option for such electron sources, and getters are placed outside of their respective image display regions.
As mentioned above, the most prolific sources of gas out of components of an image display device are an image display region, which is formed from a fluorescent film or the like and which high energy electrons impact on, and the electron source itself. Generation of gas could be prevented by thorough degasification treatment, such as slow baking at high temperature. However, in practice, thorough degasification treatment is not always successfully carried out because electron-emitting devices and other members are damaged by heat and there is a strong possibility left that gas is generated.
In the case where the gas pressure rises locally and instantly, ions accelerated by an electric field collide against other gas molecules and cause incessant ion creation, which could induce electric discharge. The electric discharge can partially destroy the electron source to degrade the electron emission characteristic. Gas generated from an image display member causes electron emission after the image display device is built and it starts rapid discharge of gas of water or the like contained in the phosphor. This can lead to apparent lowering in luminance of an image at an early stage after the start of driving. As driving is continued, now the periphery of the electron source too discharges gas and the characteristic is degraded gradually. When a getter region is provided only on the outside of the display region as in prior art, gas generated near the center of the image display region takes long to reach the outside getter region and, moreover, is re-adsorbed by the electron source before adsorbed by the getter. Therefore the getter region cannot exert a significant effect in preventing degradation of the electron emission characteristic and lowering in luminance of an image is particularly noticeable at the center of the image display region.
On the other hand, when a getter member is placed to remove generated gas quickly inside an image display region of a flat panel display that does not have the above gate electrode or control gate, lowering in luminance of an image is noticeable outside the image display region because of gas generated outside of the display region.
In the case where a getter activation method shown in JP 09-82245 A is employed, heater wiring dedicated to getter activation is laid out to complicate the simplified process again. If a getter is activated by electron beam irradiation, load is applied to an electron beam to degrade the electron source while the display device is not driven.